1. Field of the Invention
The present invention relates generally to devices for injecting materials into the earth""s subsurface. In particular, the present invention relates to drivable probes used for injecting materials into the subsurface for remediating soil and ground water contamination, stabilizing soil, and making other geotechnical improvements.
2. Description of the Related Art
The use of direct push techniques to inject chemicals into the subsurface for the remediation or clean up of contaminated ground water and soil gained notoriety in the mid to late 1990s. The use of small diameter tools as a conduit to deliver remediation materials into contaminated, subsurface zones can be an efficient method to remediate contaminated soils.
To date, the bulk of injection work is being done with equipment and techniques designed for hole abandonment grouting. As shown in FIG. 1, this particular technique uses a probe assembly 10 having a point 11 that closes off the leading end 12 of the tool string 13. After the initial investigation (e.g., soil sampling, ground water sampling, etc.) the open probe hole 14 must be properly sealed with a suitable grout mix 15 to prevent migration of contaminated soils throughout the probe hole 14.
The conventional tool string 13 is first advanced to the bottom of the open probe hole 14. The tool string 13 is then retracted allowing the point 11 (often referred to as the xe2x80x9cexpendable pointxe2x80x9d) to fall off leaving the inside diameter (xe2x80x9cIDxe2x80x9d) of the tool string 13 open to the soil. A grout mix 15 is then pumped through the ID of the tool string 13 as the tool string 13 is retracted out of the probe hole 14. The probe hole 14 is filled to the top as the tool string 13 is retracted. This particular approach is commonly referred to as xe2x80x9cbottom up grouting.xe2x80x9d
Remediation materials are often delivered in this same manner. The problem with injecting remediation materials with this technique is ensuring that the material is evenly injected into the soil throughout the entire injection interval. As the tool string 13 is retracted and material is being injected, the resistance to material flow into the soil will change as the geological characteristics change. This can lead to more material being injected into zones. 16, 18 with less resistance to flow and less material going into zones 17 with a higher resistance to flow. For this reason, the use of a xe2x80x9ctop down injectionxe2x80x9d approach is more advantageous.
FIG. 2 illustrates an injection probe assembly 20 for use in a top down injection technique. The top down injection approach uses a reduced diameter injection area 21 along the sheath 22 of the probe assembly 20 to define an injection interval. The defined injection area 21 on the sheath 22 eliminates the open hole below the tool string where the injected material would be exposed to differing soil with varying resistances to flow, as in the bottom up grouting and injection techniques shown in FIG. 1. The top down injection approach ensures that the material is being injected evenly over the entire injection interval.
A difficulty in top down injection techniques is the lack of tooling available for such an approach. Since the injection takes place during several advancements of the tool string 24, clogging of the sheath 22 or the tool string 24 is often a problem. In addition to clogging, the soil around the injection point 25 can resist flow, causing pressure to build up in the soil formation and inside the tool string 24. This excess formation pressure causes the material 23 being injected to flow back up through the tool string 24 where it is displaced through the top of the tool string 24 and spills onto the ground at the top of the probe hole.
Thus, there is a need in the industry for an improved tool string for use in top down injection techniques which eliminates clogging and prevents back-flow of injection material.
It is an object of the present invention to provide an injection probe that solves the above-described problems with existing top down injection techniques.
It is a further object of the present invention to provide an injection probe that ensures material is injected evenly over the desired interval, that prevents the tool string from clogging during normal string advancement, and that prevents back-flow of the injection material up the tool string when pressure develops within the soil formation.
It is a further object of the present invention to provide an improved pressure activated injection probe that can be used effectively to provide uniform top down injection into the subsoil without clogging, and that is economical to manufacture, capable of a long operating life, and particularly well suited for use in remediating contaminated soils and ground water.
In order to solve the problems with the prior art described above, the applicant has developed an improved pressure activated injection probe assembly for injecting materials into subsurface formations to remediate contaminated soils and ground water, to inject grout materials for soil stabilization, and for making other geotechnical improvements. The probe assembly includes a sheath having an upper end for attaching to a mating tool string and a lower end for receiving a solid drive point. The sheath has a reduced diameter injection area which includes an interior space enclosed by a tubular sidewall, a valve seat, and at least one and preferably a plurality of injection ports extending through the sidewall through which materials can be injected laterally. A check valve spool is arranged for sliding movement within the interior space of the sheath for preventing clogging and back-flow of material into the interior space. The valve spool has a first closed position in which an upper end thereof is seated on the valve seat and an outer cylindrical surface covers the inner sides of the injection ports. The valve spool has a second open position in which the upper end is unseated from the valve seat and the injection ports are open to the interior space. The valve spool is biased toward its closed position by a compression spring, and is responsive to pressure changes within the sheath for movement between the closed and open positions.
According to a broad aspect of the present invention, an injection probe is provided, comprising: a tubular assembly having an upper end for attaching to a mating tool string, a lower end for receiving a solid drive point, an upper seal portion adjacent to the upper end, a lower seal portion adjacent to the lower end, and an injection area between the upper and lower seal portions. The injection area has a smaller outer diameter than the upper and lower seal portions, an interior space enclosed by a tubular sidewall, a valve seat, and at least one and preferably a plurality of injection ports extending through the sidewall through which materials can be injected laterally into a subsurface formation. A check valve spool is arranged for sliding movement within the interior space of the injection area for preventing back-flow of material into the interior space. The check valve spool has a first position in which an end portion of the check valve spool is seated on the valve seat and an outer surface of the check valve spool covers the injection ports and prevents material from flowing back into the interior space through the injection ports. The valve spool has a second position in which the end portion of the check valve spool is unseated from the valve seat and the injection ports are open to the interior space.
Numerous other objects of the present invention will be apparent to those skilled in this art from the following description wherein there is shown and described a preferred embodiment of the present invention, simply by way of illustration of one of the modes best suited to carry out the invention. As will be realized, the invention is capable of other different embodiments, and its several details are capable of modification in various obvious aspects without departing from the invention. Accordingly, the drawings and description should be regarded as illustrative in nature and not restrictive.